1. Field of the Invention
The present invention relates to a dielectric resonator, a dielectric filter and a wireless communication system using the dielectric filter.
2. Description of the Related Art
In recent years, communication systems for millimeter wave bands such as wireless LAN have been studied, and at the same time, passive devices used for such systems have been eagerly studied.
As a conventional multilayer-type dielectric resonator used for millimeter wave bands, a dielectric resonator having a rectangular multilayer waveguide structure as shown in FIGS. 18(a) and 18(b) has been proposed. This dielectric resonator comprises a dielectric substrate 1 including a plurality of stacked dielectric layers, a lower conductor 4b and an upper conductor 4a disposed to be in contact with the dielectric substrate 1, a conductor 2 disposed in a layer inside the dielectric substrate 1 which has a rectangular resonance aperture area 3, and via conductors 5 connecting the lower conductor 4b to the upper conductor 4a. The via conductors 5 enclose the resonance aperture areas 3 thereby to constitute the dielectric resonator. The resonance mode is TE10 mode in which an electric field perpendicular to the lower and upper conductors 4b and 4a is generated. In this structure, size reduction is achieved as compared to conventional waveguide structures.
It is possible to compose a multilayer-type dielectric filter with input/output sections by connecting input and output terminals of the dielectric resonator to the dielectric resonator by means of irises of the via conductors. In addition, it is also possible to accomplish coupling of dielectric resonators by connecting a plurality of dielectric resonators having the same structure to one another by means of irises of the via conductors.
There is also proposed a TE010 mode dielectric resonator as a dielectric resonator of a type that has a space utilized for millimeter wave bands. As shown in FIG. 19, this dielectric resonator includes a dielectric substrate 1 in a central area of a space surrounded by metal conductors 4a and 4b. Conductor plates 2a and 2b are disposed on and under the dielectric substrate 1 to be in contact with the dielectric substrate 1, and the conductor plates 2a and 2b are provided with circular resonance aperture areas 3a and 3b, respectively, so that a part of the dielectric is exposed. This dielectric resonator is utilized for filters for millimeter wave bands.
Meanwhile, challenges in passive devices for millimeter wave bands are miniaturization and cost reduction. When technologies used in mass production of applications for microwave bands are applied to those for millimeter wave bands, due to the small sizes of the parts, the machining accuracy fails to respond to the small sizes. This results in an increase in unit price of the parts.
To take the case of the multilayer dielectric resonator used for millimeter wave bands (FIG. 18), if misalignment occurs in the arrangement of the via conductors 5, the resonant frequency may deviate from the designed value. The variation in resonance frequency represents the difference between the design value of the dielectric filter and that after the production of the same. For this reason, it is necessary to arrange a great number of via conductors in the dielectric resonator with high accuracy. Therefore, producing dielectric resonators with high yield is difficult without adjustments, leading to high costs.
Also, in the case of the aforesaid dielectric resonator with a space (FIG. 19), if misalignment of the axes of the resonance apertures 3a and 3b occurs, the resonant frequency may deviate from the designed value. This variation in resonant frequency represents the difference between the design value of the dielectric filter and that after the production of the same. It is predicted that as the size of the resonance apertures becomes smaller, the deviation of the resonant frequency from the design value associated with misalignment of the axes of the upper and lower resonance aperture areas increases.
It is an object of the present invention to provide a dielectric resonator, a dielectric filter and a wireless communication system using the dielectric filter that allow the accuracy for designing resonant frequencies to be greatly improved.
It is another object of the present invention to provide a dielectric resonator, a dielectric filter and a wireless communication system using the dielectric filter that allow the production process to be simplified and the cost to be reduced.